1. Field of the Invention
The present invention relates to a propylene resin composition which has a good balance between impact resistance, and rigidity and surface hardness. The present invention also relates to a novel method for evaluating a propylene resin composition, which can be effectively used for providing a propylene resin composition having a good balance of the above properties.
2. Background Art
Propylene resins possess excellent moldability, paintability and mechanical strength and, by virtue of these features, have hitherto been mass-produced for use as materials for various molded products in the filed of industrial parts, for example, automobile parts, such as bumpers, instrument panels, trims, center pillars, door trims, fan shrouds, and glove boxes, and parts for domestic electric appliances, such as televisions, VCRs, and washing machines.
The recent trend in the above application fields towards highly functional, large-sized articles often requires the parts of such articles to be thinner and to have complicated shapes. Such parts should desirably possess well-balanced rigidity and impact resistance.
In order to improve the impact resistance of propylene resins, addition or copolymerization of various rubber components has generally been carried out. In this case, however, the rubber component is generally so soft that the resultant composition is likely to become excessively soft. Molded products of such compositions have a low surface hardness and therefore are easy to be marred. Thus, the conventional propylene resin compositions can hardly satisfy both the impact resistance and surface hardness requirements.
A propylene resin composition has thus been desired which has high impact strength without suffering from the excessive lowering in rigidity and surface hardness.
It is therefore an object of the present invention to provide a propylene resin composition that has a good balance between rigidity and surface hardness, and impact strength.